Industrial or commercial incinerators that burn waste or trash provide a source of energy that can be utilized to heat a fluid, such as air or water, in an energy recovery system. In a conventional energy recovery system, as used in the past, hot flue gases from the incinerator were discharged into a vertical stack and the lower end of the stack was connected to a steam or a hot water boiler, so that a portion or all of the flue gases could be drawn through the boiler to heat the water. In the conventional system, a fan was located in the gas discharge line from the boiler and served to draw the gases through the boiler and the flow of gas was controlled by a damper located in the discharge line. The damper, in turn, was controlled by the boiler pressure, in the base of a steam boiler, and boiler temperature, in the case of a hot water boiler, with the flow of flue gas being varied to maintain the desired thermal characteristics of the boiler.
The conventional energy recovery systems, as described above, were capable of generating steam or hot water only during periods when the incinerator was operating, and during periods when waste was not being burned in the incinerator, as for example overnight or weekends, no steam was generated. Thus, the incinerator heat recovery system could not be relied on to supply all of the steam or hot water requirements, and auxiliary steam or hot water generating facilities were normally required.